1. Optimizing Geometry for Efficient Rendering Real Time Rendering Instructor: David Luebke

2. Immediate Mode glBegin(GL_TRIANGLES); glVertex3f(…); glEnd(); –Easy, flexible, good match for early hardware –Slow on current hardware  Bus-limited, API-limited  Hard to parallelize with strict ordering semantics

3.  How fast can you call glVertex3fv?  On my laptop, 15M/sec  Two conditional branches  13(+) memory accesses!  Upwards of 800MB/sec to the memory system 695480A0 push esi 695480A1 mov eax,fs:[00000BF0] 695480A7 test byte ptr [eax+3F5Fh],10h 695480AE je 695480E2 695480B0 lea edx,[eax+3640h] 695480B6 mov esi,dword ptr [esp+8] 695480BA mov dword ptr [edx+0Ch],3F800000h 695480C1 mov ecx,dword ptr [esi] 695480C3 mov dword ptr [edx],ecx 695480C5 mov ecx,dword ptr [esi+4] 695480C8 mov esi,dword ptr [esi+8] 695480CB mov dword ptr [edx+4],ecx 695480CE mov ecx,eax 695480D0 mov dword ptr [edx+8],esi 695480D3 mov edx,3 695480D8 call dword ptr [eax+0BFA8h] 695480DE pop esi 695480DF ret 4 695480E2 mov edx,dword ptr [eax+477F0h] 695480E8 mov esi,dword ptr [esp+8] 695480EC mov ecx,dword ptr [esi] 695480EE mov dword ptr [edx],0C2C00h 695480F4 mov dword ptr [edx+4],ecx 695480F7 add edx,10h 695480FA mov ecx,dword ptr [esi+4] 695480FD mov dword ptr [eax+477F0h],edx 69548103 mov esi,dword ptr [esi+8] 69548106 mov dword ptr [edx-8],ecx 69548109 mov dword ptr [edx-4],esi 6954810C cmp dword ptr [eax+477F4h],edx 69548112 ja 69548121 69548114 xor edx,edx 69548116 mov ecx,dword ptr [eax+477D0h] 6954811C call 6950EAE0 69548121 pop esi 69548122 ret 4 Immediate Mode: glVertex()

4. Triangle Strips  Ideally, approach 1 vertex/triangle –Implication: long strips better than short –Less T&L, less memory/bus bandwidth, less API function overhead  Triangle fans: same idea  Triangle strip subtleties –Switching direction –Degenerate triangles

5. Display Lists  Display lists were the solution –Compilation of rendering calls –Can be re-executed w/ a single call –Can include other display lists  Potential savings: –Memory layout –API calls (less run-time error checking etc) –Even functional savings (e.g. folding matrices)

6. Vertex Arrays  List of vertices in an array –Separate –Interleaved –Can render from subarrays  Compiled vertex arrays  Indexed vertex arrays –Bandwidth –Vertex cache

7. Vertex Cache  What is the optimal way to render this mesh if you have an 8-vertex cache?

8. Efficient Vertex Arrays  Memory –System –AGP –Video  VAR & VBO  Locking semantics  Fence semantics